I have a similar problem. When my brake light went out I replaced the bulb. That seemed to fix the problem BUT now when I turn on the headlamps and step on the brake that brake and tail light goes out. What happened? I have a similar problem. When my brake light went out I replaced the bulb. That seemed to fix the problem BUT now when I turn on the headlamps and step on the brake that brake and tail light goes out. What happened?

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GM had a lot of problems with the circuit boards that house the rear lights. My suggestion is to use a test light clip one end to the trucks body parts then remove brake light switch the orange wire should light the bulb on test light this is the power wire, the white wire is the stop light circuit with switch out this also should be lite up. Drop down turn signal switch connector the brake lamp wire goes up the turn signal switch and comes back down the yellow and green wires no power there it is a bad turn signal switch. If Ok Now remove one tail lamp assembly unplug harness and test for power if still have no power trace wiring back to fire wall and check at bulkhead connector. IF ok then circuit board is bad.

Assuming this has the V6, the 15A PARK LPS fuse in the underhood fuse block feeds constant power to the auto park lamp relay. When the relay closes, 12V power passes through the 10A INST LPS fuse in the right instrument panel fuse block to the panel dimmer switch and then to the five instrument cluster lamps.

If by "rear lights" you mean everything in the rear lamp assemblies, power for the tail lights (running lights) starts at the 15A PARKLAMP fuse in the underhood junction block, passes through the automatic lamp control (ALC) relay and the right instrument panel junction block to the tail filament of the dual stop/tail lamp and the separate tail lamp on each side. The 12 V power for the stop lamps is protected by the 20A STOPLAMPS fuse in the left I/P junction block, passes through the stoplamp switch when brakes are applied, stop filament of the dual stop/tail lamps. That leaves the turn signals and the hazard lamps. Power for the turn signals originates at the 10A TURNLAMPS fuse in the left I/P junction block and is applied to the hazard switch. Switch output goes to the turn/headlamp/wiper switch for selection of left or right turn signals. That switch output goes to the turn lamp. Power for the hazard function begins at the 10A HAZRD LPS fuse in the left I/P junction box and goes to the hazard switch. Switch output is sent to the left I/P junction box to make the turn signals flash. That's it. Post a comment if you need more information.

Check your fuses underneath the drivers side steering wheel. Flip the plastic cover over and there will be a diagram showing the fuse that controls the taillights/stoplamp. Pull the fuse out and replace it with the same number fuse and your taillights and brake lights will work again. If the fuses are ok, pull each taillight bulb out and replace it with a new bulb. Sometimes when one light bulb fails, all of them will fail.

OK ... being as you've ripped the entire interior out things might be easier to disconnect now .... I suspect the dash light dimmer assembly (I don't remember but this vehicle may even have a dimmer fuse??? check the owners manual ...) which goes to many lights and if damaged shows a dead short (has the radio ever been changed?) I would first disconnect the dimmer assembly (cluster lamps) (that will eliminate that circuit) replace the fuse and try turning the parking lamps on ... if the fuse blows again ... it's not the dimmer cicuit ... then ... You will measure a short when checking continuity between negative battery terminal and the light circuit as the filaments in the lamps will read continuity but it should show some resistance and not a dead short under normal conditions. I would then disconnect the harnesses going to the rear of the car located in the left kick panel and or the right kick panel .... the way you will solve it is to work one section at a time ... and a bunch of fuses ... trial and error then focus on the suspect section ... the thing that gets me is: you say the short goes away (on the meter) when the brakes are applied or left turn signal. So it might be in the rear harness ... I would also inspect the left rear light assembly and the harness to it (possibly a bad ground) good luck and let me know what you find

These are Dual Function Bulbs. They control the Parking Lights and the Brake Lights. This Bulb is Burnt out on the Brake Coil inside the Bulb. I have actually seen Bulbs that were Bad But you could not Tell by jast looking at them. It should be fine with a New Bulb. Please Rate My Response! Thanks!